1. Field of the Invention
The present invention relates to a small sized anode, and a magnetron therewith.
2. Background of the Related Art
In general, the magnetrons, as a kind of vacuum tube, have applications to micro-ovens, plasma lighting apparatuses, dryers, and other high frequency systems owing to merits of simple structure, high efficiency, and stable operation, and the like.
Upon application of a power to the magnetron, thermal electrons are emitted from a cathode, and the thermal electrons generate microwaves by action of a strong electric field, and a strong magnetic field applied between the cathode and an anode. The microwave generated thus is transmitted from an antenna, and used as heat source for heating an object.
A system of the magnetron will be described briefly, with reference to FIG. 1.
Referring to FIG. 1, there are an anode 10 inside of the magnetron, and a cathode 15 of a helical filament 14 in an inner central part of the anode 10.
The anode 10 is provided with a cylindrical anode body 11, a plurality of vanes 12 attached to an inside wall of the anode body 11 in a radial direction, and straps 13 on upper and lower surfaces of the vanes 12.
In the straps 13, there are inner straps 13a and outer straps 13b each in contact with every second vanes 12 alternately for electrical connection of the vanes 12. The antenna 16 is attached to one of the vanes 12 for emitting a high frequency energy transmitted to the anode 10 to an exterior.
Along with this, there are a resonance cavity between adjacent vanes 12, and an interaction space between the cathode 15 and the vane 12. There are upper and lower magnetic poles 20a and 20b for being magnetized by magnets 19a and 19b to generate a magnetic energy.
There are a plurality of cooling fins 17 on an outer circumferential surface of an anode body 11 for dissipating heat from the anode body 11 to an exterior, and upper and lower yokes 18a and 18b at an outside of the cooling fins 17 for holding and protecting the cooling fins 17 and guiding an external air to the cooling fins 17.
Of the different components of the related art magnetron, the anode 10 will be described in more detail.
Referring to FIGS. 2A and 2B, the cylindrical anode body 11 with an inside diameter Dbi has the plurality of vanes 12 each with a thickness Vt and a height Vh attached thereto in the radial direction. Opposite fore ends of the vanes 12 are spaced a distance Da apart from each other. The inner straps 13a and the outer straps 13b are provided to the upper part and the lower part of the vanes 12, each with a thickness St and a distance Siso between the two straps 13a and 13b. 
The related art magnetron is operative as follows.
When a power is provided to the cathode 15, thermal electrons are emitted from the filament 14 and positioned in the interaction space. Along with this, the magnetic field formed by one pair of the magnets 19a and 19b is focused to the interaction space by one pair of the magnetic poles 20a and 20b. 
Consequently, the thermal electrons are caused to make a cycloidal motion by the magnetic field, which generates a microwave having a high frequency energy. The microwave is transmitted from an antenna 16 attached to the vane 12.
The microwave transmitted thus cooks or heats food when the magnetron is applied to a microwave oven, or emits a light as the microwave excites plasma when the magnetron is applied to lighting.
Meanwhile, the high frequency energy failed in the transmission to an outside of the anode 10 is dissipated as heat to an exterior by the cooling fins 17 around the anode body 11.
The related art magnetron is failed in an optimal design, with waste of material. That is, even though cost of the magnetron can be reduced substantially if the oxygen-free copper used in the anode of the related art magnetron is reduced while maintaining performance of the magnetron, there are no researches for this.
Particularly, the part of the related art magnetron that has the highest possibility of a product cost reduction is the anode, because the anode has the greatest expected effect of the cost reduction in that, if a cylindrical inside diameter Dbi of the anode is reduced even a little, a reduction of size is a multiple of π (3.14) to the reduced size.
At the end, a necessity of a technology that can reduce the inside diameter Dbi of the anode while maintaining a performance of the magnetron is known.